Repair process for aluminum and magnesium articles

ABSTRACT

Damaged articles formed of aluminum or magnesium, including the alloys thereof, are repaired by suitably preparing the damaged area as, for example, grinding away the fault; refilling the prepared area utilizing a plasma spray repair coating comprising aluminum or an aluminum-silicon alloy with a mixture of 10-40 weight percent molybdenum; and subsequently refinishing to dimension, if required.

- 10d States Patent 1 Leeper, J r.

1 1 Jan. 16, 1973 [54] REPAIR PROCESS FOR ALUMINUM AND MAGNESIUM ARTICLES [75] lnventor: Henry 1P. Leeper, Jra, Madison,

Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

22 Filed: Ju1y26,l97l

21 Appl.No.: 164,877

[52] U.S. Cl. ..1 17/2, 29/401, 29/527.4, 29/DIG. 39, 117/22, 117/105 [51] Int. Cl. ..B23p 7/00 [58] Field of Search...29/401, 527.2, 527.4, DIG. 39; 117/105, 2, 22

[56] References Cited UNITED STATES PATENTS 2,588,422 3/1952 Shepard ..117/105 X 3,004,336 10/1961 Timuska .....29/401 3,077,659 2/1963 Holzwarth et a1. 3,107,175 10/1963 Cape 3,382,085 5/1968 Wrcn ct a1. ..117/22 X Primary Examiner-Charles W. Lanham Assistant Examiner-Donald C. Reiley, 111 Attorney-Richard N. James [57] ABSTRACT 3 Claims, N0 Drawings REPAIR PROCESS FOR ALUMINUM AND MAGNESIUM ARTICLES BACKGROUND OF THE INVENTION aluminum or magnesium (including the alloys thereof wherein aluminum and/or magnesium comprise the predominant constituents) minor faults are often generated either in the production process itself or as a result of damage in service. Frequently, the faults are of such nature that repair would be possible if an economical and otherwise satisfactory repair process existed. Conventional repair techniques at best require a two step process, i.e., a bond coat followed by a repair coat. The direct single step plasma spray coating techniques utilizing coating materials identical or galvanically similar to the basis metal have generally been unsatisfactory. And this appears to be true despite the fact that plasma spray coatings of various types have heretofore been referenced in the art, as evidenced, for example, by the patent to Dittrich et al. US. Pat. No. 3,436,248.

SUMMARY OF THE INVENTION This invention contemplates a repair process for aluminum or magnesium articles wherein:

the surface to be repaired, after any necessary machining, is cleaned;

a mixture of powders comprising, by weight, 10-40 percent molybdenum together with 60-90 percent aluminum, or aluminum/silicon alloy containing up to percent silicon, is plasma sprayed on the area to be repaired to effect the necessary buildup; and

the part is subsequently processed to finished dimen- SlOl'lS.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the typical plasma spray coating process a powdered coating material, suspended in a suitable carrier gas, is fed into a chamber in which flowing gas has been excited or heated to extremely high temperatures by an electric are or oxy-hydrogen or oxy-acetylene flame. Coating particles are heated to plasticity and carried onto the workpiece in the resulting high velocity plasma stream of ionized gas which issues from the nozzle of the specially constructed torch. The usual carrier gas is argon or helium, although for the coating of aluminum or magnesium up to percent by volume hydrogen may be added.

In the typical repair process, the defect to be repaired is removed by appropriate machining techniques except, of course, in the case where the fault is merely the result of undersizing Subsequently, the part is cleaned to remove all dirt, grease and other foreign matter and the surface is prepared for application of the repair coating by grit blasting preferably using nonmetallic grit. Coating on the cleanest possible surface is preferred and coating is normally commenced within at least 2 hours of cleaning and blasting.

Usually the parts are preheated to remove moisture and to minimize thermal shock and thermal expansion effects during the actual coating operation. In coating, however, special care is taken to prevent bulk overheating and during the spraying operation, the average temperature of the part is limited to a maximum of about 400F.

Coatings of various compositions applied at various plasma power levels have been made, the results of which are summarized in the following tables.

Table I AMS 4117 Aluminum Alloy To A Repair Coating Thickness Of 0.0l0-0.0l2 Inch Thickness Plasma Bond Strength Power Level (psi) Plasma Powder (kw) 0.0l0-0.0l2" Thick Coating Pure Al I0 2740 Pure Al 12 2850 Pure Al 14 2650 Pure Al 16 3060 Al+l5 w/o Mo 12 4470 Al+15 w/o Mo 16% 6290 Al+27 w/o Mo 10 4440 Al+27 w/o Mo 16% 5230 Al+37 w/o M0 10 5650 Al+37 w/o Mo 12 4490 Al+37 w/o Mo 14 5250 Al+37 w/o Mo I6 5590 Table II AMS 4375 Magnesium Alloy Bond Strength Coating (Average psi) Pure Aluminum I730 Al+l5% Mo 2500 All2% Si Alloy 3670 All2% Si Al+l5% Mo 4430 The usual acceptable minimum bond strength for repair processes of this nature on aluminum is 3000 p.s.i. As will be noted, the bond strengths of the Al (l5-40)Mo (020)Si repair coatings of the present invention are all considerably in excess of this minimum. Typical powder sizes utilized were 200 mesh for molybdenum and l 325 mesh for the aluminum.

Salt spray tests on coated parts have also been conducted with only minor pitting of the repair area noted in 1,000 hours on AMS 4026 aluminum sheet.

Thus, it has been established that aluminum and magnesium articles may be economically and satisfactorily repaired in a process incorporating but a single plasma spray coating step.

The invention in its broader aspects is not limited to the specific details described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. A process utilizing a single spray coating step for the repair of defects in articles formed of aluminum or magnesium, which process comprises the steps of:

cleaning the surface to be repaired;

in a single step, plasma spray coating the cleaned surface in order to effect the necessary coating buildup, using a coating mixture which consists of finely divided powders of a composition which consists essentially of, by weight, l0-4O percent molybdenum and 60-90 percent aluminum containing 0-20 percent silicon;

and, subsequently, processing the part to restore it to dimension.

2. The process according to claim 1 wherein:

the article is preheated to a temperature of 200-400 F. for the plasma spray coating step. 5

3. The process according to claim 2 wherein:

the bulk temperature of the article during plasma spray coating is limited to 400F. maximum. 

2. The process according to claim 1 wherein: the article is preheated to a temperature of 200*-400*F. for the plasma spray coating step.
 3. The process according to claim 2 wherein: the bulk temperature of the article during plasma spray coating is limited to 400*F. maximum. 